Press molding and its high frequency quenching method and its high frequency quenching system

ABSTRACT

A press formed article such as a center pillar or the like for a vehicle having a demanded strength distribution achieved by hardening through induction hardening or the like, and a method and an apparatus for performing induction hardening on the press formed article. The center pillar ( 10 ) being a press formed article has an intermediate top portion ( 11 ) which extends in a longitudinal direction of the center pillar ( 10 ), and two blade portions ( 12 ) which are both bent in the same direction from both sides of the intermediate top portion ( 11 ), in which hardening regions (Q) are provided on both sides of the intermediate top portion ( 11 ), extending over the intermediate top portion ( 11 ) and the blade portions ( 12 ). These hardening regions (Q) hardened by the induction hardening apparatus are regions in a form which widens toward the end and continuously expand from the upper portion to the lower portion of the center pillar ( 10 ). Therefore, the ratio between the hardening regions and non-hardening regions changes in the longitudinal direction of the center pillar ( 10 ), resulting in a demanded strength distribution.

TECHNICAL FIELD

The present invention relates to a press formed article which has beensubjected to hardening treatment, and an induction hardening method andan induction hardening apparatus therefor, and is applicable to, forexample, various kinds of press formed articles such as a center pillar,a front bumper beam, a front side frame, a door reinforcing material,and so on of a vehicle.

BACKGROUND ART

A center pillar, which is a vehicle body part forming a part of avehicle body of a four-wheel vehicle and is a column between a frontseat and a back seat, is formed to have a cross section in the form of ahat by the press forming of a sheet metal. Specifically, the centerpillar is a press formed article and is composed of: an intermediate topportion which extends in a longitudinal direction which is also avertical direction; a pair of blade portions which are both bent fromthe intermediate top portion toward the inside of the vehicle in adirection perpendicular to the longitudinal direction within the surfaceof the intermediate top portion, that is, on both sides in afront-and-rear direction of the vehicle, and extend in the longitudinaldirection, with a direction of the bend being a direction of the widththereof; and flange portions which extend in the front-and-reardirection of the vehicle away from each other, from tips of the bladeportions. This center pillar is formed in an elongated shape having asmall dimension of the width in the front-and-rear direction of thevehicle to ensure a wide field of vision from the cabin through thewindow glass of a side door, but required a high strength for measuresagainst a side collision with other vehicles, walls, and so on.

To increase the strength of the center pillar, there are well-knownconventional ways such as the provision of a reinforcement such as areinforcing material at the center pillar, or hardening treatment on thecenter pillar.

The former way results in an increase in the whole weight of the centerpillar and is against the demand for a smaller vehicle weight, andaccordingly, the latter way is more preferable. In the latter way, whenperforming hardening treatment on the center pillar, it is desirable toperform hardening treatment to be able to achieve a demanded strengthdistribution by providing a high strength at a position where the highstrength is required and to provide a low strength at a position wherethe low strength is sufficient, in order to effectively receive a loadacting on the center pillar.

Japanese Patent Laid-Open No. Hei 10-17933 is well known as a prior artmethod of performing such a hardening treatment. In this prior artmethod, a hardening treatment is performed on the center pillar acrossthe entire width in the front-and-rear direction of the vehicle by aninduction hardening apparatus. By this hardening treatment, the hardnessdistribution in the vertical direction is made to correspond to ademanded strength distribution. In order to achieve such a hardnessdistribution, when the hardening treatment is performed while moving theinduction hardening apparatus with respect to the center pillar, themoving speed is changed.

In this prior art, the way for achieving the demanded strengthdistribution is to create in the center pillar a hardness distributioncorresponding to the strength distribution. To achieve such a hardnessdistribution corresponding to the strength distribution requires a highlevel technology including control technology in consideration ofvarious kinds of conditions such as a material and so on of the centerpillar.

It is an object of the present invention to provide a press formedarticle such as a center pillar or the like whose demanded strengthdistribution can be easily achieved by hardening treatment, and toprovide an induction hardening method and an induction hardeningapparatus for use in producing this press formed article.

DISCLOSURE OF THE INVENTION

A press formed article according to the present invention is a pressformed article including: an intermediate top portion which extends in alongitudinal direction; and a pair of blade portions which are both bentfrom the intermediate top portion on both sides in a directionperpendicular to the longitudinal direction within a surface of theintermediate top portion, and extend in the longitudinal direction, witha direction of the bend being a direction of the width thereof,characterized in that a hardening region where hardening has beenperformed and a non-hardening region where hardening has not beenperformed are provided within at least the pair of blade portions out ofthe intermediate top portion and the pair of blade portions, and that anarea ratio between the hardening region and the non-hardening region inthe width direction is a ratio for achieving a demanded strength.

In this press formed article, the hardening region and non-hardeningregion are provided within at least the pair of blade portions out ofthe intermediate top portion and the pair of blade portions, and thearea ratio between the hardening region and the non-hardening region inthe width direction is a ratio for achieving a demanded strength.Therefore, the degree of strength can be determined by the setting ofthe ratio between the hardening region and the non-hardening region, sothat a demanded strength distribution can be easily achieved. Further,the non-hardening region can ensure a tenacity corresponding to theratio of the non-hardening region to the hardening region.

In this press formed article, when the strength is not changed in thelongitudinal direction of the press formed article to make the strengthdistribution uniform in the longitudinal direction, the ratio betweenthe hardening region and the non-hardening region does not need to bechanged in the longitudinal direction of the press formed article. Onthe other hand, when the strength is changed in the longitudinaldirection of the press formed article to make the strength distributionnot uniform, the ratio between the hardening region and thenon-hardening region only needs to be changed in the longitudinaldirection of the press formed article. In the latter case, it is alsopossible to provide a portion which is made a hardening region or anon-hardening region, at a part in the longitudinal direction of thepress formed article.

Further, the hardening region may also be provided in the intermediatetop portion. When the hardening region is provided also in theintermediate top portion as described above, the hardening region may beprovided over the whole intermediate top portion in the directionperpendicular to the longitudinal direction within the surface of theintermediate top portion, or the hardening region may be provided onlyon both sides of the intermediate top portion in the direction, and anon-hardening region may be provided between the hardening regions.

According to the latter, the non-hardening region can ensure thetenacity of the press formed article. Further, the non-hardening regioncan also be formed with a hole. It should be noted that when thehardening energy in hardening is in no danger of concentrating to thesurroundings of the hole, the hole may be provided in the hardeningregion. Further, in this case, the non-hardening region does not need tobe provided in the intermediate top portion.

Further, a press formed article according to the present invention is apress formed article including: an intermediate top portion whichextends in a longitudinal direction; and a pair of blade portions whichare both bent from the intermediate top portion toward the same side onboth sides in a direction perpendicular to the longitudinal directionwithin a surface of the intermediate top portion, and extend in thelongitudinal direction, with a direction of the bend being a directionof the width thereof, characterized in that a hardening region wherehardening has been performed and a non-hardening region where hardeninghas not been performed are provided within at least the intermediate topportion out of the intermediate top portion and the pair of bladeportions, and that an area ratio between the hardening region and thenon-hardening region in the direction perpendicular to the longitudinaldirection within the surface of the intermediate top portion is a ratiofor achieving a demanded strength.

In this press formed article, the hardening region and non-hardeningregion are provided within at least the intermediate top portion out ofthe intermediate top portion and the pair of blade portions, and thedegree of the strength can be determined by the setting of the arearatio between the hardening region and the non-hardening region in thedirection perpendicular to the longitudinal direction within the surfaceof the intermediate top portion, so that a demanded strengthdistribution can be easily achieved also in this press formed article bythe setting of the ratio between the hardening region and thenon-hardening region. Further, the non-hardening region can ensure atenacity corresponding to the ratio of the non-hardening region to thehardening region.

Also in this press formed article, the strength does not need to bechanged in the longitudinal direction of the press formed article by notchanging the ratio between the hardening region and the non-hardeningregion in the longitudinal direction of the press formed article.Alternatively, the strength may be changed in the longitudinal directionof the press formed article by changing the ratio between the hardeningregion and the non-hardening region in the longitudinal direction of thepress formed article. In the latter case, it is also possible to providea portion which is made a hardening region or a non-hardening region, ata part in the longitudinal direction of the press formed article.

Further, the hardening region to be provided in the intermediate topportion may be provided only on both sides in the directionperpendicular to the longitudinal direction within the surface of theintermediate top portion, and the non-hardening region may be providedbetween the hardening regions.

The non-hardening region can ensure tenacity of the press formedarticle. Further, the non-hardening region can also be formed with ahole. It should be noted that, also in this press formed article, whenthe hardening energy in hardening is in no danger of concentrating tothe surroundings of the hole, the hole may be provided in the hardeningregion.

A first example of the press formed article to be subjected to hardeningtreatment as described above is a center pillar of a vehicle. It ispreferable to provide the hardening region at a portion of the centerpillar corresponding to a window hole for inserting therein a windowglass in a side door of the vehicle.

According to this, a demanded strength against a side collision withother vehicles, walls, and so on, can be imparted to a portion of thecenter pillar which is small in the width dimension in thefront-and-rear direction of the vehicle to ensure a wide vision from thecabin through the window glass of the side door.

Further, the hardening region of the center pillar may be a regionhaving a uniform strength distribution from an upper portion to a lowerportion, and may also be a region in the form, widening toward an end,which continuously expands from an upper portion to a lower portion.

According to the latter, the strength of a point receiving a large sidecollision load from other vehicles and so on can be made high, and thecollision energy can be effectively absorbed by a portion which ishigher than the point and whose strength gradually decreases. Further,the hardening region continuously expands and has no portion sharplychanging in shape. Therefore, the strength distribution neither changessharply to prevent the center pillar from being folded when receiving acollision load from other vehicles and so on.

It should be noted that the shape of the hardening region of the centerpillar is not limited to the above but is, for example, a region in theform, widening toward an end, which continuously expands from a lowerportion to an upper portion in accordance with the strength of thevehicle body based on the internal structure of the vehicle, or adiscontinuous region in which the hardening region is removed at pointsto which side door hinges are attached.

The center pillar, in which a portion corresponding to a window hole forinserting therein a window glass in the side door is subjected tohardening treatment, may be provided with reinforcement at an upperportion and a lower portion of the hardening region. The reinforcementprovided at the upper portion of the hardening region can ensure a greatstrength of joining with roof portions of other members which constitutethe vehicle body. The reinforcement provided at the lower portion of thehardening region can increase the strength of points to which side doorhinges are attached.

Note that depending on the kind of a vehicle using the center pillar inwhich the portion corresponding to the window hole for inserting thereina window glass in the side door is subjected to hardening treatment asdescribed above, one reinforcement out of the reinforcement provided atthe upper portion and the lower portion of the hardening region, forexample, the upper reinforcement, may be omitted.

Further, the center pillar may be provided with a reinforcement havingthe same or almost the same length as that of the range in thelongitudinal direction of the center pillar provided with the hardeningregion. According to this, the whole weight of the center pillarincreases, but the whole strength of the center pillar can be madehigher by the increment of strength resulting from the hardeningtreatment than that of another center pillar having the same wholeweight.

A second example of the press formed article to be subjected tohardening treatment is a front bumper beam of a vehicle. It ispreferable that the hardening region of the front bumper beam is madelarge at combined portions on both right and left sides to which tips ofright and left front side frames of the vehicle are combined, and isgradually decreased toward a middle portion between the right and leftsides.

According to this, when a light collision load acts on the middleportion of the front bumper beam having a whole shape in the form of abow in which the middle portion between the right and left sides bulgesforward, the load can be effectively received by the middle portionwhich is not so high in strength but is high in tenacity. A largecollision load can be effectively received by the right and leftcombined portions which have high strengths and to which the front sideframes are combined.

A third example of the press formed article to be subjected to hardeningtreatment is a front side frame of a vehicle whose tip portion iscombined to a front bumper beam. It is preferable that the hardeningregion of the front side frame is made large at the tip portion and at aportion at a position retreating from the tip portion with an intervaltherefrom, and is small at a middle portion therebetween.

According to this, when a large collision load from the front bumperbeam acts on the front side frame, the middle portion having a lowstrength can be a buckling point where buckling is caused, so that itscollision energy can be effectively absorbed by the front side frameowing to the buckling point.

It should be noted that the shape of the hardening region provided inthe front side frame is not limited to the above and is arbitrary, andby arbitrarily setting the shape of the hardening region, the positionof the buckling point can be set arbitrarily.

In addition to the above, the press formed article to be subjected tohardening treatment may be a reinforcing member for a side door of avehicle or a reinforcing member for a back door, also called a tailgate, or may be side sills joined to right and left end portions of afront floor, a rear side frame, or a rear side frame reinforcement.Further, when a reinforcement is provided at the center pillar, thisreinforcement may be applied, and accordingly, the press formed articleto which the present invention is applied may be an arbitrary pressformed article.

Further, the press formed article related to the present invention maybe a press formed article for other than a vehicle, for example, for anelectrical appliance.

Further, the hardening apparatus for performing hardening treatment onthe press formed article may be an induction hardening apparatus, alaser hardening apparatus, a gas flame hardening apparatus, and thus maybe an arbitrary type hardening apparatus.

An induction hardening method for a press formed article according tothe present invention is characterized by including: a first step ofmanufacturing a press formed article including: an intermediate topportion which extends in a longitudinal direction, and a pair of bladeportions which are both bent from the intermediate top portion in adirection perpendicular to the longitudinal direction within a surfaceof the intermediate top portion, and extend in the longitudinaldirection, with a direction of the bend being a direction of the widththereof; a second step of heating a hardening region by at least oneinductive conductor of a heating inductor for induction hardening havinga size capable of heating the whole of the hardening region at once toprovide the hardening region where hardening has been performed, and anon-hardening region where hardening is not performed, at an area ratiofor achieving a demanded strength, within at least the intermediate topportion out of the intermediate top portion and the pair of bladeportions of the press formed article; and a third step of rapidlycooling the hardening region to thereby perform induction hardening onthe hardening region.

According to this induction hardening method, since at least oneinductive conductor of a heating inductor for induction hardening has asize capable of heating the whole of the hardening region at once, theinduction hardening can be performed in a short time by quickly heatingthe whole of the hardening region by the inductive conductor and rapidlycooling the hardening region, resulting in achievement of improvedefficiency of the hardening operation.

In this induction hardening method, the dimension of the inductiveconductor in the direction perpendicular to the longitudinal directiondoes not need to be changed or may be changed in the longitudinaldirection. When it is changed, for this change, the area ratio betweenthe hardening region where induction hardening has been performed andthe non-hardening region where hardening is not performed can be changedin the longitudinal direction, so that a press formed article can beobtained in which the strength distribution is changed in thelongitudinal direction.

When a hole needs to be provided in the intermediate top portion at amiddle portion between both sides in the direction perpendicular to thelongitudinal direction within a surface of the intermediate top portion,this hole is formed in the step of manufacturing the press formedarticle, and thereafter positions on both sides of the intermediate topportion in the direction perpendicular to the longitudinal directionwithin the surface of the intermediate top portion and other than thehole, are heated by two inductive conductors of the heating inductor forinduction hardening.

According to this, the positions subjected to the induction hardeningare provided away from the position where the hole is formed, andtherefore induction hardening energy never concentrates to thesurroundings of the hole in induction heating by the inductiveconductors to prevent generation of unevenness in hardening. It shouldbe noted that when the induction hardening energy is in no danger ofconcentrating to the surroundings of the hole, the position where thehole is formed may also be heated.

An induction hardening apparatus for a press formed article according tothe present invention is characterized by including: at least oneinductive conductor of a heating inductor for induction hardening forproviding a hardening region where hardening has been performed withinat least an intermediate top portion out of the intermediate top portionand a pair of blade portions in a press formed article including theintermediate top portion which extends in a longitudinal direction, andthe pair of blade portions which are both bent from the intermediate topportion in a direction perpendicular to the longitudinal directionwithin a surface of the intermediate top portion, and extend in thelongitudinal direction, with a direction of the bend being a directionof the width thereof; a power supply device for applying a highfrequency current to the heating inductor for induction hardening; and acooler for rapidly cooling the hardening region which has beeninductively heated by the inductive conductor, wherein the inductiveconductor has a size capable of heating the whole of the hardeningregion at once, and the size of the inductive conductor is a size forachieving a demanded strength by an area ratio between the hardeningregion where induction hardening has been performed by the inductiveconductor and the cooler and a non-hardening region where hardening isnot performed.

According to this induction hardening apparatus, since at least oneinductive conductor of a heating inductor for induction hardening has asize capable of heating the whole of the hardening region at once, thewhole of the hardening region can be quickly heated by the inductiveconductor, and the hardening region is rapidly cooled, whereby theinduction hardening can be performed in a short time, resulting inefficient performance of the hardening operation.

The cooler in the induction hardening apparatus may be an apparatus forspraying a cooling medium such as cooling water or the like to at leastthe hardening region of the press formed article, or may be an apparatusfor immersing the whole press formed article in a cooling liquid. In thecase of the apparatus for spraying the cooling medium, the cooler can besimplified.

Further, in this induction hardening apparatus, the dimension of theinductive conductor in the direction perpendicular to the longitudinaldirection does not need to be changed or may be changed in thelongitudinal direction. When it is changed, for this change, the arearatio between the hardening region where induction hardening has beenperformed and the non-hardening region where hardening has not beenperformed is changed in the longitudinal direction, so that a pressformed article can be manufactured in which the strength distribution ischanged in the longitudinal direction.

Further, it is preferable that the inductive conductor of the heatinginductor and a feed line used in this hardening apparatus are composedof a hollow cylindrical conductor and inside thereof is a cooling waterpassage. According to this, the inductive conductor and so on can becooled by a simple structure.

It is preferable that an inductive face of the heating inductor isprovided with an insulating coating. This makes it possible to preventshort circuiting, even though the heating inductor accidentally touchesthe hardening region when the heating inductor is disposed closely andopposed to the hardening region of the intermediate top portion in thepress formed article, leading to safety.

Further it is also recommendable to dispose on the inductive face of theheating inductor a spacer for controlling the distance with respect tothe hardening region. The provision of such a spacer allows the opposingdistance between the inductive face of the heating inductor and thehardening region to be a desired value when the heating inductor isdisposed closely and opposed to the hardening region, only by disposingthe heating inductor in such a manner to push it to the hardening regionthrough the spacer, thereby facilitating the operation of disposing theheating inductor.

Further, the spacer is made of an insulating material to contribute toenhancement of insulation between the inductive conductor and thehardening region.

Further, the number of the heating inductors in the width direction ofthe hardening region may be one, or plural side by side in the widthdirection, in accordance with the width dimension of the hardeningregion. Further, the latter may be realized by turning back an elongatedheating inductor at end portions in the longitudinal direction of thehardening region to reciprocate in the longitudinal direction. Accordingto this, the power supply device for supplying electricity to theheating inductor can be one in number.

It is preferable that the cooler is disposed on a side opposite to theheating inductor with respect to front and rear sides of the pressformed article, and has a configuration provided with a cooling pipe forspraying a cooling medium to the whole of the hardening region at once.This configuration enables cooling without interfering with the heatinginductor. In addition, the whole of the hardening region can be cooledin a short time and uniformly.

Note that it is also possible to arrange the inside of the heatinginductor to be a passage in which the cooling medium flows to spray thecooling medium from the heating inductor to the press formed article.According to this, the heating inductor can be also used as the cooler.Further the arrangement of the inside of the heating inductor having apassage in which the cooling medium flows can also be implemented in thecase of a cooling pipe for spraying the cooling medium being provided onthe side opposite to the heating inductor with respect to front and rearsides of the press formed article as described above.

If the cooling medium is a liquid such as cooling water or the like,this cooling liquid is sprayed to the hardening region and thereafterflows outside the press formed article. Therefore, it is preferable thatthe press formed article is disposed inside a pan for receiving thecooling liquid sprayed onto the hardening region and flowing outside thepress formed article. This facilitates treatment of the cooling liquidafter cooling the hardening region.

Further, it is also preferable that the pan forms a part of acirculation path for circulating therein the cooling liquid. Thisenables reuse of the cooling liquid. In such a case of reuse of thecooling liquid, a part of the cooling liquid is lost due to evaporationaccompanying the spraying onto the hardening region heated to hightemperature. Therefore, a cooling liquid replenishing pipe may beprovided along the circulation path to be able to replenish the lostcooling liquid.

Further, it is preferable that the circulation path is provided with adissolved oxygen removing means for removing oxygen dissolved in thecooling liquid circulating in the circulation path. According to this,since the cooling liquid sprayed onto the hardening region has thedissolved oxygen removed, hardening can be performed with the preventionof oxidation on the side of a face sprayed with the cooling liquid inthe hardening region, so that a post-operation for the coating and so onconducted on the press formed article after hardening, can be conductedas predetermined.

An example of the dissolved oxygen removing means is designed to includea blow pipe for blowing an anti-oxidation gas such as nitrogen gas orthe like into the cooling liquid stored in a storage tank, so that theblow removes dissolved oxygen dissolved in the cooling liquid.

Note that the dissolved oxygen removing means is not limited to one forcompletely removing the dissolved oxygen from the cooling liquid, butmay be one capable of removing the dissolved oxygen from the coolingliquid to a degree at which the post-operation to be conducted afterhardening can be conducted without trouble.

If the above-described post-operation for the coating and so on isconducted after hardening, it is preferable that the hardening apparatusis provided with an anti-oxidation gas supply means for performinghardening of the hardening region in an anti-oxidation gas atmosphere.This makes it possible to harden the hardening region with prevention ofoxidation, so that the post-operation can be conducted as predetermined.

When an inside space of the elongated intermediate top portion of thepress formed article is in the anti-oxidation gas atmosphere, and atleast one end portion out of both end portions in a longitudinaldirection along the intermediate top portion of the inside space is opento be an open end, it is preferable that an anti-oxidation gas jet meansis provided at the open end to form a gas curtain made of ananti-oxidation gas at the open end.

According to this, the gas curtain can prevent the anti-oxidation gassupplied from the anti-oxidation gas supply means into the inside spaceof the intermediate top portion from flowing out from the open end so asto keep the anti-oxidation gas atmosphere in this inside space. Further,also in the case of spraying the cooling liquid in the inside space, thecooling liquid after the spraying is allowed to flow out from the openend.

When the hardening apparatus is provided with a cover for covering anoutside of the press formed article, with a distance space between thecover and the press formed article being in the anti-oxidation gasatmosphere, and at least one end portion out of both end portions in alongitudinal direction along the intermediate top portion of thedistance space is open to be an open end; it is preferable that ananti-oxidation gas jet means is provided at the open end to form a gascurtain made of an anti-oxidation gas at the open end.

According to this, the gas curtain can prevent the anti-oxidation gassupplied from the anti-oxidation gas supply means into the distancespace from flowing out from the open end so as to keep theanti-oxidation gas atmosphere in this distance space.

In the above description, “anti-oxidation” of the anti-oxidation gas isnot limited to the meaning of completely preventing the oxidation of thehardening region, but also includes the meaning of suppressing theoxidation to a low level, and thus oxidation at a level at which thepost-operation can be conducted as predetermined is allowable.

Further, after the hardening region is heated by application andstoppage of the current to the inductive conductor of the heatinginductor for induction hardening, spraying and stopping of the coolingliquid from the cooling pipe to the hardening region may be conducted.Alternatively, after start of the spraying of the cooling liquid fromthe cooling pipe to the hardening region, application and stoppage ofcurrent to the inductive conductor may be conducted, and subsequentlythe spraying of the cooling liquid may be stopped.

Further, it is also possible that the pan is a water tank fully storingtherein the cooling liquid having dissolved oxygen removed, and thepress formed article is set in this water tank in a manner so as to besubmerged therein, and in this state, hardening may be performed on thehardening region by application of current to the inductive conductor.In this arrangement, the anti-oxidation gas supply means becomesunnecessary.

Furthermore, the hardening apparatus may be an apparatus provided with achamber fully filled with an anti-oxidation gas in which hardening isperformed on the press formed article. Moreover, the hardening apparatusmay be an apparatus provided with a standby chamber coupled to achamber, so that a press formed article, which will be hardened next,stands by in this standby chamber for continuous hardening of aplurality of press formed articles.

The above-described present invention is applicable to manufacturing ofa press formed article from a steel sheet having an arbitrary tensilestrength. This tensile strength may be at the 441.29925 N/mm² level,490.3325 N/mm² level, 588.399 N/mm² level, 686.4655 N/mm level, or784.532 N/mm² level.

However, when using, as a material of the press formed article, a steelsheet at the 441.29925 N/mm² level in tensile strength, this tensilestrength being not so high, a product in a complex shape can bemanufactured by press working. Therefore, even if a press formed articleto be manufactured is in a complex shape, this press formed article canbe manufactured as predetermined by press working.

Further, when using, as a material of the press formed article, a steelsheet at the 441.29925 N/mm² level in tensile strength, the hardeningtemperature can be a relatively low temperature, 900° C. or lower, forexample, a temperature within a range from 750° C. to 900° C. Inparticular, when a hardening temperature is within a range from 800° C.to 850° C., this hardening temperature never breaks a galvanized layerof a galvanized steel sheet as well as can ensure a predeterminedstrength by the hardening. This makes it possible to obtain also astrength required as a vehicle body part or the like using as thematerial of the press formed article the galvanized steel sheet which iseffective against rust.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing a side body on the left side out ofright and left side bodies of a four-wheel vehicle in which a centerpillar being a press formed article according to an embodiment of thepresent invention is used;

FIG. 2 is a cross-sectional view taken along a line S2—S2 in FIG. 1;

FIG. 3 is a front view of the whole center pillar which is shown on arelation with an inner panel out of an outer panel and the inner panelforming the side body in FIG. 1;

FIG. 4 is an essential portion enlarged view of the center pillarshowing a portion subjected to hardening treatment;

FIG. 5 is a cross-sectional view taken along a line S5—S5 in FIG. 4;

FIG. 6 is a cross-sectional view taken along a line S6—S6 in FIG. 4;

FIG. 7 is a cross-sectional view taken along a line S7—S7 in FIG. 4;

FIG. 8 is a perspective view showing a general configuration of aninduction hardening apparatus when set on the center pillar;

FIG. 9 is a view, similar to FIG. 2, showing an embodiment in which areinforcement across a range in the longitudinal direction of the centerpillar provided with the hardening regions is provided at the centerpillar;

FIG. 10 is a perspective view showing a front bumper beam and a rightand left pair of front side frames before combination;

FIG. 11 is a plan view showing the front bumper beam and the right andleft pair of front side frames after the combination;

FIG. 12 is a side view showing the front bumper beam and the right andleft pair of front side frames after the combination;

FIG. 13 is a cross-sectional view taken along a line S13—S13 in FIG. 11;

FIG. 14 is a cross-sectional view taken along a line S14—S14 in FIG. 11;

FIG. 15 is a cross-sectional view taken along a line S15—S15 in FIG. 11;

FIG. 16 is a cross-sectional view taken along a line S16—S16 in FIG. 12;

FIG. 17 is a cross-sectional view taken along a line S17—S17 in FIG. 12;

FIG. 18 is a cross-sectional view taken along a line S18—S18 in FIG. 12;

FIG. 19A is a schematic perspective view showing a press formed articleto be subjected to induction hardening, and 19B is a schematiccross-sectional view of the press formed article;

FIG. 20 is a schematic perspective view showing the state of the pressformed article in FIG. 19 mounted on a support;

FIG. 21 is a schematic perspective view showing the state of the pressformed article in FIG. 19 mounted on the support and a heating inductorfor induction hardening disposed closely to the press formed article;

FIG. 22 is a schematic cross-sectional view showing the state of theheating inductor for induction hardening disposed closely to a hardeningregion set in the press formed article in FIG. 19 and cooling pipesdisposed inside the heating inductor;

FIG. 23 is a schematic cross-sectional view of a ridge portion of thepress formed article in FIG. 19 and the heating inductor for inductionhardening disposed closely thereto;

FIG. 24 is a schematic cross-sectional view showing the press formedarticle and the heating inductor in FIG. 23, cut along the ridgeportion;

FIG. 25A is a schematic plan view of the press formed article in FIG.19, and FIG. 25B is a schematic cross-sectional view showing the pressformed article and the heating inductor, cut along the ridge portion;

FIG. 26 is a graph showing hardness distributions within a hardeningregion which is subjected to hardening in Examples 1 and 2;

FIG. 27 is a side cross-sectional view showing a more specificembodiment of a hardening apparatus, a view showing it including acooling water circulation path and a supply path of anti-oxidation gas;

FIG. 28 is an enlarged view of an essential portion in FIG. 27; and

FIG. 29 is a cross-sectional view taken along a line S29—S29 of FIG. 28.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in more detail with reference to theaccompanying drawings. FIG. 1 shows a side body 1 for the left side outof right and left side bodies of a four-wheel vehicle in which a centerpillar being a press formed article according to an embodiment of thepresent invention is applied. The side body 1 is formed by joining anouter panel on the outside of the vehicle and an inner panel on theinside of the vehicle. In addition, in the side body 1, a center pillar10 according to this embodiment is disposed in an inner space 4 which isformed by center pillar portions 2A and 3A, between a front seat and arear seat, of an outer panel 2 and an inner panel 3 as shown in FIG. 2which is a cross-sectional view taken along a line S2—S2 in FIG. 1.

This center pillar 10 is composed of: an intermediate top portion 11which extends in a vertical direction and a longitudinal direction; apair of blade portions 12 which are both bent from the intermediate topportion 11 toward the inside of the vehicle in a direction perpendicularto the vertical direction within the surface of the intermediate topportion 11, that is, on both sides in a front-and-rear direction of thevehicle, and extend in the vertical direction, with a direction of thebend being a direction of the width thereof; and flange portions 13which extend in the front-and-rear direction of the vehicle away fromeach other from the tips of the blade portions 12. Therefore, the centerpillar 10 has a cross section in the form of a hat.

FIG. 3 shows a front view of the whole center pillar 10, in which theinner panel 3 is shown with the outer panel 2 removed. Upper and lowerend portions of the center pillar 10 are formed with bulge portions 14and 15 which bulge out in the front-and-rear direction of the vehicle,and as a result, the whole shape of the center pillar 10 is an almost Ishape. The center pillar 10 to be installed between the outer panel 2and the inner panel 3 is combined to the outer panel 2 and the innerpanel 3 by joining the upper and lower bulge portions 14 and 15 to aroof portion and a floor portion of the outer panel 2 and to a roofportion 3C and a floor portion 3D of the inner panel 3, and joining theflange portions 13 shown in FIG. 2 to a flange portion 2B of the centerpillar portion 2A of the outer panel 2 and to a flange portion 3B of thecenter pillar portion 3A of the inner panel 3, respectively by spotwelding.

Further, as shown in FIG. 3, reinforcements 16 and 17 are disposed atthe upper portion of the center pillar 10 and at an almost middleportion or at a portion slightly lower than that in the verticaldirection, and the reinforcements 16 and 17 are joined to the centerpillar 10 by spot welding.

As shown in FIG. 2, the intermediate top portion 11 of the center pillar10 is formed with a hole 18. A plurality of holes 18 are provided in thelongitudinal direction of the intermediate top portion 11 as shown inFIG. 3. These holes 18 are provided for the purpose that when the sidebody 1, which is formed by the outer panel 2, the inner panel 3, thecenter pillar 10, the reinforcements 16 and 17, and other necessaryparts, is immersed in an electro-deposition coating liquid forelectro-deposition coating, the electro-deposition coating liquidentering the inner space 4 which is formed by the center pillar portions2A and 3A of the outer panel 2 and the inner panel 3 is securely causedto enter a narrow gap 5 between the center pillar portion 2A of theouter panel 2 and the center pillar 10 so that the inner face of thecenter pillar portion 2A of the outer panel 2 can be securelyelectro-deposition coated as predetermined.

In the above arrangement, the center pillar 10 is manufactured bytransfer pressing a non-plated steel sheet or a galvanized steel sheet11.0 mm, 1.2 mm, 1.4 mm, or 1.6 mm in thickness and 441.29925 N/mm² intensile strength, and in manufacturing by this transfer press work, theholes 18 are formed by punching.

FIG. 4 is an essential portion enlarged view showing a portion which isto be subjected to hardening treatment of the center pillar 10 formedwith the holes 18 as described above. Hardening regions Q whose outlinesare shown by two-dotted chain lines 19 are provided between thereinforcements 16 and 17, partially overlapping the reinforcements 16and 17. FIG. 5 is a cross-sectional view taken along a line S5—S5 inFIG. 4, FIG. 6 is a cross-sectional view taken along a line S6—S6 inFIG. 4, and FIG. 7 is a cross-sectional view taken along a line S7—S7 inFIG. 4. As understood by FIG. 4 to FIG. 7, the hardening regions Q areprovided in the intermediate top portion 11 and the pair of bladeportions 12, and are regions in the form, widening toward the end, whichcontinuously expands from the upper portion to the lower portion, in theintermediate top portion 11 and the pair of blade portions 12.

Besides, as shown in FIG. 4, the hardening regions Q are provided in aportion of the center pillar 10 corresponding to a window hole forinserting therein a window glass 20 (see also FIG. 3) provided in a sidedoor of the vehicle.

In this embodiment, the hardening regions Q are provided at twopositions in the front-and-rear direction of the vehicle. Regions at theintermediate top portion 11 of the hardening regions Q are provided onboth sides in the direction perpendicular to the longitudinal directionof the center pillar 10 within the surface of the intermediate topportion 11, in other words, on both sides in the front-and-reardirection of the vehicle, and these regions continue to regions in therespective blade portions 12 of the hardening regions Q.

The holes 18 shown in FIG. 4 are provided between the regions which areformed on both sides in the front-and-rear direction of the vehicle inthe intermediate top portion 11 of the two hardening regions Q providedseparately in the front-and-rear direction of the vehicle.

Within the intermediate top portion 11 and the pair of blade portions12, portions other than the hardening regions Q are non-hardeningregions where hardening is not performed. As described above, since thehardening regions Q are in the form, widening toward the end, whichcontinuously expands from the upper portion to the lower portion, thenon-hardening regions are conversely in a tapered shape whichcontinuously decreases from an upper portion to a lower portion.Accordingly, the intermediate top portion 11 and the pair of bladeportions 12 have the hardening regions Q and the non-hardening regionsrespectively. In addition, in the intermediate top portion 11, the ratiobetween the hardening regions Q and the non-hardening region in thefront-and-rear direction of the vehicle is changed in the longitudinaldirection of the center pillar 10 in such a manner that the proportionof the hardening regions Q increases as shifting from the upper portionto the lower portion. Also, in each of the pair of blade portions 12,the area ratio between the hardening region Q and the non-hardeningregion in the width direction of the blade portion 12 is changed in thelongitudinal direction of the center pillar 10 in such a manner that theproportion of the hardening region Q increases as shifting from theupper portion to the lower portion.

The above-described hardening regions Q are formed by manufacturing thecenter pillar 10 from the aforesaid galvanized steel sheet by thetransfer press work, forming the holes 18 in the manufacturing, andthereafter performing hardening treatment on the center pillar 10 by aninduction hardening apparatus.

FIG. 8 shows a general configuration of an induction hardening apparatus30. The induction hardening apparatus 30 has an oscillator 31; and apair of coil portions 32 provided in the front-and-rear direction of thevehicle which are connected to the oscillator 31 and set on the centerpillar 10 or set to oppose the center pillar 10. Therefore, theinduction hardening apparatus 30 can provide the above-describedhardening regions Q in the center pillar 10 depending on the settingsuch as the shape of the coil portions 32 provided for each of thehardening regions Q which are formed separately in the front-and-reardirection of the vehicle in the center pillar 10.

The hardening treatment by the induction hardening apparatus 30 providesthe hardening regions Q, which are hardened, shown in FIG. 4 to FIG. 7in the center pillar 10.

According to the above-described embodiment, the hardening regions Q andthe non-hardening regions are provided in the intermediate top portion11 and the pair of blade portions 12 of the center pillar 10, in whichthe strength of the center pillar 10 is decided by the ratio between thehardening regions Q and the non-hardening region in the front-and-reardirection of the vehicle in the intermediate top portion 11, and by thearea ratio between the hardening region Q and the non-hardening regionin the width direction of the blade portion 12 in the blade portions 12.Therefore, a demanded strength of the center pillar 10 can be set bythese ratios, and the strength distribution in the longitudinaldirection of the center pillar 10 can be easily set by deciding theratio between the hardening regions Q and the non-hardening regions inthe longitudinal direction of the center pillar 10.

Besides, the hardening regions Q in the center pillar 10 are provided ata portion corresponding to the window hole for inserting therein thewindow 20 provided in the side door. Although this portion of the centerpillar 10 is a portion formed in such a manner that the width thereof inthe front-and-rear direction of the vehicle is small to ensure a widevision from the cabin, the provision of the hardening regions Q in thisportion can impart to this portion a sufficient strength against a loadupon a side collision with other vehicles, walls and so on.

Further, a portion lower than the hardening regions Q is reinforced witha reinforcing beam which is installed in a portion of the side doorlower than the window glass 20, and this reinforcing beam ensures astrength against the collision load for the portion lower than thehardening regions Q. In addition, the hardening regions Q are in theform, widening toward the end, which expands from the upper portion tothe lower portion of the center pillar 10 and, accordingly, can providea high strength of a point receiving a large side collision load fromother vehicles and so on. In addition, collision energy can beeffectively absorbed by a portion which is higher than the point andwhose strength gradually decreases and whose tenacity graduallyincreases in accordance with the expansion of the non-hardening regions.

Besides, the hardening regions Q are changed continuously and notchanged sharply, and therefore, no point is produced which changessharply in strength by the hardening treatment, thus preventing thecenter pillar 10 from being folded upon reception of a collision load orthe like from other vehicles and so on.

Further, the center pillar 10 is provided with the reinforcements 16 and17 at the upper and lower portions of the hardening regions Q, so thatthe reinforcement 16 at the upper portions of the hardening regions Qcan ensure a great strength of joining with the roof portions of theaforesaid outer panel 2 and the inner panel 3 which constitute thevehicle body, and the lower reinforcement 17 at the lower portions ofthe hardening regions Q can increase the strength of points to whichside door hinges are attached. Furthermore, these reinforcements 16 and17 can eliminate a sharp drop in the strength of the center pillar 10 atthe upper and lower end portions of the hardening regions Q.

Moreover, the regions in the intermediate top portion 11 of thehardening regions Q provided in the center pillar 10 are providedseparately on both sides in the front-and-rear direction of the vehiclein the intermediate top portion 11. An intermediate portion between bothsides, that is, a portion which is the non-hardening region, is formedwith the holes 18 which become necessary at the time ofelectro-deposition coating as described above. Since the hardeningregions Q are provided on both sides in the front-and-rear direction ofthe vehicle in the intermediate top portion 11 and away from thepositions of the holes 18, the provision of the hardening regions Q inthe center pillar 10 by the induction hardening operation after theformation of the holes 18 never causes unevenness in hardening due tothe induction hardening energy concentrating to the surroundings of theholes 18.

Besides, the center pillar 10 is manufactured by conducting press workon a steel sheet which is 441.29925 N/mm² in tensile strength, and thistensile strength is not so high, so that a center pillar 10 in a complexshape can be formed in a shape as desired. In addition, the hardeningtemperature for hardening the steel sheet with the above tensilestrength only needs to be a relatively low temperature, 900° C. orlower, for example, a temperature within a range from 750° C. to 900° C.In particular, a hardening temperature within a range from 800° C. to850° C. never breaks a galvanized layer of the galvanized steel sheet aswell as can ensure a predetermined strength by the hardening. This makesit possible to achieve a strength required as the center pillar 10 usingas the material of the center pillar 10 the galvanized steel sheet whichis effective against rust.

FIG. 9 shows an embodiment in which a reinforcement 40, which has thesame or almost the same length as that of the range in the longitudinaldirection of the center pillar 10 provided with the hardening regions Q,is joined to the center pillar 10 by spot welding. According to thisembodiment, the whole weight of the center pillar 10 increases by thatof the reinforcement 40. However, this embodiment provides an advantagethat the whole strength of the center pillar 10 can be increased by theincrement of strength resulting from the provision of the hardeningregions Q in the center pillar 10, as compared to the case of anothercenter pillar having the same whole weight.

It should be noted that, in this embodiment, the reinforcement 40 may beprovided on the center pillar 10 as a member independent of thereinforcements 16 and 17 shown in FIG. 3 and FIG. 4, or may be providedon the center pillar 10 as a member having a long vertical dimension andserving also as the reinforcements 16 and 17. Alternatively, thereinforcements 16 and 17 may be superposed on and joined to thereinforcement 40 having the long vertical dimension.

FIG. 10 to FIG. 18 show an embodiment of a front bumper beam and frontside frames of a four-wheel vehicle when the hardening treatment isapplied thereto. FIG. 10 is a perspective view of a front bumper beam 50and a right and left pair of front side frames 60 before combination,FIG. 11 is a plan view after the combination, and FIG. 12 is a side viewafter the combination. FIG. 13 is a cross-sectional view taken along aline S13—S13 in FIG. 11, FIG. 14 is a cross-sectional view taken along aline S14—S14 in FIG. 11, FIG. 15 is a cross-sectional view taken along aline S15—S15 in FIG. 11, FIG. 16 is a cross-sectional view taken along aline S16—S16 in FIG. 12, FIG. 17 is a cross-sectional view taken along aline S17—S17 in FIG. 12, and FIG. 18 is a cross-sectional view takenalong a line S18—S18 in FIG. 12.

As shown in FIG. 10 to FIG. 12, on both right and left sides of thefront bumper beam 50 having a whole shape in the form of a bow in whichthe middle portion in the longitudinal direction thereof bulges forward,tip portions of the right and left pair of front side frames 60 arecombined to the front bumper beam 50 by welding or with fastening meanssuch as bolts or the like. These front side frames 60 are combined toright and left side bodies and a dashboard panel in an engine room of anFF four-wheel vehicle.

As shown in FIG. 10 and FIG. 13 to FIG. 15, the front bumper beam 50 iscomposed of: a front face portion 51 which is an intermediate topportion extending in the longitudinal direction being the lateraldirection of the vehicle; and an upper face portion 52 and a lower faceportion 53 being a pair of blade portions which are both bent toward thebackside of the vehicle in a direction perpendicular to the longitudinaldirection within the surface of the front face portion 51, in otherwords, on both upper and lower sides, with a direction of the bend beinga direction of the width thereof; and a rear face portion 54 whichcombines rear end portions of the upper face portion 52 and the lowerface portion 53. The upper face portion 52, the lower face portion 53,and the rear face portion 54 are designed to extend, similarly to thefront face portion 51, in the longitudinal direction of the front bumperbeam 50 and have a length across the whole length of the front bumperbeam 50.

Hardening regions Q provided in the front bumper beam 50, as shown inFIG. 11 showing the outlines of the hardening regions Q on the upperface portion 52 by two-doted chain lines 55 and in FIG. 13 to FIG. 15showing changes in the regions Q in the longitudinal direction of thefront bumper beam 50, are increased at combined portions on both rightand left sides to which tip portions of the right and left pair of frontside frames 60 are combined and gradually decrease toward the middleportion between the right and left sides.

Such a design of the hardening regions Q makes it possible that when alight collision load acts on the middle portion of the front bumper beam50 having a whole shape in the form of a bow in which the middle portionbetween the right and left sides bulges forward, the light collisionload can be effectively received by the middle portion which is not sohigh in strength and is high in tenacity instead because of thenon-hardening region. On the other hand, a large collision load can beeffectively received by the right and left combined portions which havehigh strengths resulting from the hardening regions Q being larger inarea than the non-hardening region and to which the front side frames 60are combined.

As shown in FIG. 10 and FIG. 16 to FIG. 18, each of the front sideframes 60 includes: a web portion 61 which is an intermediate topportion extending in the longitudinal and front-and-rear direction ofthe vehicle; and flange portions 62 and 63 being an upper and lower pairof blade portions which are both bent toward the outside of the vehiclein a direction perpendicular to the longitudinal direction within thesurface of the web portion 61, in other words, on both upper and lowersides, with the direction of the bend being the direction of the widththereof. The flange portions 62 and 63 extend, similarly to the webportion 61, in the longitudinal direction of the front side frame 60.

Hardening regions Q provided in the front side frame 60 having such ashape, as shown in FIG. 12 showing the outlines of the hardening regionsQ in the web portion 61 by two-doted chain lines 64 and in FIG. 16 toFIG. 18 showing changes in the regions Q in the longitudinal directionof the front side frame 60, are large at a tip portion combined to thefront bumper beam 50 and at a rear portion at a position retreating fromthe tip portion toward the backside of the vehicle with an intervaltherefrom, and are small at a middle portion between these portions.

Such a design makes it possible that when a large collision load acts onthe front side frame 60 from the front bumper beam 50, the middleportion having a low strength between the tip portion and the rearportion can be a buckling point where buckling is caused, so that alarge collision energy can be effectively absorbed by the front sideframe 60 due to the buckling point.

Next, a method and an apparatus for performing induction hardening onpress formed articles, including vehicle body parts such as a centerpillar and so on, are described.

A press formed article 101 shown in FIGS. 19A and 19B is produced bypress forming a steel sheet and has a shape provided with: anintermediate top portion 101A extending across the whole length thereof;flange portions 101B on both sides thereof; blade portions 101D whichare provided between the intermediate top portion 101A and the flangeportions 101B and are both bent toward the same side in a directionperpendicular to the longitudinal direction of the intermediate topportion 101A within the surface of the intermediate top portion 101A,and extend in the longitudinal direction of the intermediate top portion101A, with a direction of the bend being a direction of the widththereof, in which, between the intermediate top portion 101A and the twoblade portions 101D, ridge portions 101C are formed. Regions having asmall width set along the ridge portions 101C (portions shown byhatchings) are hardening regions 102 to be subjected to hardening.

The hardening regions 102 extend over the intermediate top portion 101Aand the blade portions 101D, and a portion between the two hardeningregions 102 in the intermediate top portion 101A is a non-hardeningregion.

In the drawing, the hardening regions 102 have a fixed width along theridge portions 101C. However, when the ratio between the hardeningregions 102 and the non-hardening region is changed along the ridgeportions 101C, in other words, along the longitudinal direction of theintermediate top portion 101A, the width dimension of the hardeningregions 102 in the direction perpendicular to the longitudinal directionof the intermediate top portion 101A is changed in the longitudinaldirection of the intermediate top portion 101A.

For application of hardening treatment to the press formed article 101,first, the flange portions 101B of the press formed article 101 aremounted on a supporting face 105A of a support 105 and fixed with fixingmembers 106 and bolts or clamps (not shown). The supporting face 105A ofthe support 105 in use here has bends matching bends of the flangeportions 101B of the press formed article 101, thereby allowing thepress formed article 101 to be fixed and held as it is in apredetermined shape. Note that if not negligible distortion occurs inthe press formed article 101 in the hardening of the press formedarticle 101, it is recommendable to design the shape of the supportingface 105A of the support 105 to be able to add to the press formedarticle a reverse distortion capable of canceling the distortion causedby the hardening when the press formed article 101 is fixed on thesupporting face 105A, or to give a reverse distortion in advance to thepress formed article 101 by appropriately disposing a spacer between thepress formed article 101 and the supporting face 105A when mounting thepress formed article 101 thereon. Such a reverse distortion is given inadvance to cancel the distortion caused by the hardening, whereby ahardened press formed article in a desired shape with little or nodistortion can be obtained.

Note that the hardening treatment may be performed without clamping orwith loosely clamping the press formed article to allow the press formedarticle to freely become deformed during heating for the hardening.

Then, as shown in FIG. 21 and FIG. 22, heating inductors 111 forinduction hardening are disposed closely to cover most of the hardeningregions 102 which are set in the ridge portions 101C of the intermediatetop portion 101A of the press formed article 101, and cooling pipes 113capable of spraying cooling water at once to the whole of the regionsheated by the heating inductors 111 are disposed inside the press formedarticle 101. The heating inductors 111 in use here include inductiveconductors 112 which are formed of hollow cylindrical conductors such ascopper pipes or the like, and formed in a shape capable of being alongthe ridge portions 101C on both sides of the intermediate top portion101A, respectively through an almost fixed distance. The shape of thecross section of the inductive conductor 112 is described below. Theheating inductors 111 disposed on both sides have ends coupled to eachother in such a configuration capable of application of current theretoand flowing water therethrough, by means of a coupling member 114 whichis composed of a hollow conductor, and the other ends provided withconnecting pipes 115 which are composed of hollow conductors. Theconnecting pipes 115 are connected to a power supply device (not shown)which applies a high frequency current to the heating inductors 111 andcoupled to supply and drainage pipes of the cooling water. Thus, theheating inductors 111 have a configuration to be supplied with a highfrequency current by the power supply device as well as with coolingwater flowing in the hollow inside thereof so that the heating inductors111 themselves are cooled.

Next, the shape of the cross section of the heating inductor 111 (theshape of the cross section in a face across the intermediate top portion101A with the heating inductor 111 disposed opposing the hardeningregion 102) is described. As shown in FIG. 23, the inductive conductor112 of the heating inductor 111 includes an inductive face 112A opposingthe hardening region 102 set in the press formed article 101. The shapein the direction across the intermediate top portion 101A of theinductive face 112A is made a shape following a face shape of thehardening region 102. This configuration allows an opposing distance Dof the inductive conductor 112A with respect to the hardening region 102to be even in the direction across the intermediate top portion 101A.The opposing distance D is made even as described above, so that heatcan be inputted, by the application of a high frequency current to theheating inductor 111, to the region opposing the inductive face 112A ofthe press formed article 101 almost evenly across the entire widththereof. It is preferable to set the distance D here normally to about 1mm to about 4 mm to enhance the heat input efficiency. A width W1 of theinductive face 112A of the heating inductor 111 is set to be almost thesame as a width W2 of the hardening region 102. It is preferable topreviously form an insulating coating 117 such as an alumina sprayedcoating at least on the inductive face 112A opposing the hardeningregion of the inductive conductor 112. The formation of the insulatingcoating 117 makes it possible to prevent short circuiting even thoughthe heating inductor 111 touches the press formed article 101 when theheating inductor 111 is disposed closely to the press formed article101.

As understood from the above explanation, the inductive conductor 112having the inductive face 112A opposing the hardening region 102corresponds in size to the hardening region 102, and therefore, theinductive conductor 112 has a size capable of heating the whole of thehardening region 102 at once.

When the heating inductor 111 is disposed closely to the press formedarticle 101, the distance D between the inductive face 112A of theheating inductor 111 and the hardening region 102 of the ridge portion101C is normally made fixed in the width direction of the heatinginductor 111 (the direction across the intermediate top portion 101A) asshown in FIG. 23, and is also made fixed in the longitudinal direction(the longitudinal direction of the intermediate top portion 101A) asshown in FIG. 24. The distance D, however, may have a configurationappropriately changed for adjusting the maximum arrival temperature orthe like. As a method of holding the heating inductor 111 so that theinductive face 112A thereof has a predetermined distance D with respectto the hardening region 102 of the ridge portion 10C, a method can beproposed in which the heating inductor 111 is held by a suitable holdingmember (not shown), and the holding member is positioned at a desiredposition with respect to the support 105. Alternatively, it is alsoadoptable to employ a method of disposing an appropriate insulatingspacer between the heating inductor 111 and the hardening region 102 ofthe ridge portion 101C, and pushing the heating inductor 111 to thehardening region 102 through the spacer. In the case of using thespacer, the spacer is preferably attached to the face 112A opposing thehardening region 102 of the heating inductor 111 for facilitation of theoperation of arranging the heating inductor 111. This spacer isadvantageous particularly when controlling the distance of the heatinginductor 111 with respect to the press formed article 101 which ismounted with a reverse distortion given.

As described above, after the heating inductors 111 are disposed closelyto the press formed article 101, the power supply device (not shown)applies a high frequency current to the heating inductors 111 toinductively heat the whole of the hardening regions 102 at the twopoints of the press formed article 101 at once, thereby raising thehardening regions 102 in temperature to be able to harden them.Subsequently, the application of the current is stopped, and the coolingwater is sprayed from the cooling pipes 113 to the hardening regions 102to cool them rapidly. Thereby, the whole of the hardening regions 102 atthe two points are hardened at once. Here, as shown in FIG. 23, theinductive face 112A opposing the hardening region 102 of the pressformed article 101 of the heating inductor 111 is made to be in a shapefollowing the face shape of the hardening region 102 in the directionacross the intermediate top portion 101A and the distance D therebetweenis made even, so that when a high frequency current is applied to theheating inductor 111, the whole of the hardening region 102 opposing theinductive face 112A is allowed to generate heat almost evenly, andaccordingly, the whole of the hardening region 102 can be raised intemperature to almost the same maximum arrival temperature in a shorttime. The induction heating by the heating inductor 111 is performed ina time as short as possible to reduce, as much as possible, heat at aheat generating portion spreading to a region adjacent thereto by heatconduction. If the hardening region 102 is slowly raised in temperatureby the heating inductor 111 by decreasing the speed of temperature rise,the heat at the heat generating region spreads to the surroundings byheat conduction to cause the outside of the hardening region 102 to bealso raised in temperature to such a temperature at which it ishardened. As a result, the hardened region spreads out to the outside ofthe hardening region 102 which is to be hardened intentionally, and inaddition, the spread might be nonuniform or the hardened region might benonuniform between products. Hence, the temperature raising time isdecreased to thereby suppress as much as possible the heat conduction tothe surroundings, thereby making it possible to apply hardening only tothe hardening region 102 which substantially corresponds to the regionopposing the inductive face 112A of the heating inductor 111. As aresult of checking by the present inventors, an excellent result couldbe provided by setting the induction heating time to 10 seconds orshorter, more desirably, 5 seconds or shorter.

The frequency of the high frequency current application to the heatinginductor 111 is preferably set in a range from 1 kHz to 50 kHz which arewidely used for normal induction heating, and more preferably, afrequency within a relatively low frequency range from 5 kHz to 25 kHzis used. Within the low frequency range, the distance D between theinductive face 112A of the heating inductor 111 and the hardening region102 exerts a small effect on the heat input amount. Therefore, afrequency within the range enables uniform heating even with a littleunevenness in the distance D, thus providing an advantage offacilitating arrangement of the heating inductor 111.

In the above-described embodiment, the opposing distance D of theinductive face 112A of the heating inductor 111 with respect to thehardening region 102 is made fixed in both the width direction and thelongitudinal direction of the heating inductor 111 to raise thehardening region 102 in temperature to an almost uniform temperature.However, since the heat spreads to the adjacent region by heatconduction in the induction heating of the hardening region 102, thetemperature tends to lower at the peripheral region of the hardeningregion 102, and particularly at both end regions in the longitudinaldirection. Therefore, if the distance of the inductive face 112A withrespect to the hardening region 102 is fixed, the uniformity intemperature can not be ensured in some cases. In such a case, it isrecommendable to vary the distance of the inductive face 112A withrespect to the hardening region 102 depending on places to make thetemperature uniform. For example, the distance of the heating inductor111 with respect to the hardening region 102 can be set smaller at bothend portions in the longitudinal direction of the intermediate topportion 101A than at the middle portion to increase the heat inputamount at both end portions for uniformity of the temperature.

In the above-described embodiment, the hardening region 102 is raised intemperature to a uniform temperature to uniformly harden the wholethereof, thereby achieving a uniform hardening hardness. When thehardening hardness of the hardening region 102 is desired to changealong the intermediate top portion 101A, the distance between theinductive face 112A of the heating inductor and the hardening region 102can be changed along the intermediate top portion 101A to change themaximum arrival temperature along the intermediate top portion 101A, ora cooling condition (for example, the amount of cooling water) can bechanged along the intermediate top portion 101A, so as to achieve adesired hardness distribution.

For example, in FIG. 25A, when it is desired to make the hardeningregion 102 lower in hardening hardness at both end portions 102A than ata middle portion 102B to make smaller the difference in hardness of thehardening region 102 with respect to regions with no hardening appliedthereto, it is only required to set, as shown in FIG. 25B, distances D′between the inductive face 112A of the heating inductor 111 and thehardening region 102 at both end portions 102A wider than the distance Dat the middle portion 102B, or by setting the amount of cooling watersmaller at both end portions 102A than at the middle portion 102B,thereby making the hardening hardness lower at both end portions 102Athan at the middle portion 102B.

EXAMPLE 1

The heating inductors 111 having a cross section in the form shown inFIG. 23 and a width W1=12 mm were disposed, with an opposing distanceD=3 mm, above the hardening regions 102 set in the ridge portions of thepress formed article 101 made of a steel sheet 1.4 mm in thickness inthe form shown in FIG. 19 and FIG. 23. A high frequency current wasapplied to the heating inductors 111 at a frequency of 8 kHz for 5seconds to raise them in temperature to a range from 850° C. to 950° C.,and immediately thereafter the cooling water was sprayed thereto tothereby perform hardening. After the completion of the hardening, thehardening hardness distribution of the hardening regions 102 in thewidth direction thereof, was measured. An example thereof is shown inFIG. 26. Note that FIG. 26 shows data of a half portion in the widthdirection of the hardening region of one of the ridge portions, in whichthe horizontal axis indicates the position in the width direction of thehardening region 102 with the middle in the width direction of thehardening region as a reference point (ordinate 0), and the verticalaxis indicates the hardness.

EXAMPLE 2

The heating inductors 111 which are the same as those in Example 1 weredisposed, with an opposing distance D=3 mm, above the hardening regions102 set in the ridge portions of the press formed article 101 the sameas that in Example 1. A high frequency current was applied to theheating inductors 111 at a frequency of 8 kHz for 8 seconds to raisethem in temperature to a range from 850° C. to 950° C., and immediatelythereafter the cooling water was sprayed thereto to thereby performhardening. After the completion of the hardening, the hardening hardnessdistribution in the width direction, was measured for results shown inFIG. 26.

As is clear from the graph shown in FIG. 26, in both Examples 1 and 2,the regions opposing the heating inductors 111 of the ridge portions101C could be hardened at an almost fixed hardness. However, while aregion having a substantially high hardness was produced outside theregion having the fixed hardness in Example 2, the hardness was steeplylowered in Example 1. From the fact, it was confirmed that the reducedheating time allows hardening to be performed only on the regionsopposing the heating inductors 111.

The hardening treatments of the above-described Examples 1 and 2 weretried by application of a high frequency current at 25 kHz, and resultsnot so different from the above examples were obtained.

FIG. 27 to FIG. 29 show a hardening apparatus according to a morespecific embodiment, and this hardening apparatus is designed to be ableto perform hardening on the hardening regions 102 of the press formedarticle 101 in an anti-oxidation gas atmosphere. FIG. 27 is a sidecross-sectional view of the hardening apparatus shown including acirculation path of the cooling water and a supply path of theanti-oxidation gas, FIG. 28 is an enlarged view of an essential portionin FIG. 27, and FIG. 29 is a cross-sectional view taken along a lineS29—S29 in FIG. 28. In the description hereinafter, components havingthe same functions or operations as those of members and devices whichhave been already described, are assigned the same reference numerals.

In FIG. 27, a pan 121 is set on a base 120, and the support 105 isdisposed inside the pan 121, in which the press formed article 101 isset on the supporting face 105A being the upper face of the support 105.The press formed article 101 is fixed to the supporting face 105A by aclamping force of a not shown booster mechanism type clamping devicesuch as a toggle mechanism or the like which acts on the fixing member106. By releasing clamping of the clamping device which is an automaticdevice or a manual operation device, the press formed article 101 can beremoved from the supporting face 105A.

Above the press formed article 101, a cover 122 is provided which isshown also in FIG. 28 and FIG. 29, and the cover 122 covering theoutside of the press formed article 101 is attached to a high frequencypower supply device 125 through stays 123 and a bracket 124. The highfrequency power supply device 125 is, as shown in FIG. 27, hung from anarm 127 of a column 126 stood from the base 120 through guide rails 128.By operating a handle 129, the high frequency power supply device 125and the cover 122 are moved in the lateral direction in FIG. 29 guidedby the guide rails 128 so as to be adjusted in position. Further, thearm 127 in FIG. 27 is disposed on a guide portion 126A of the column 126in such a manner to be freely vertically slidable by expansion andcontraction of a cylinder 130.

The cover 122 covering the upper side of the press formed article 101,as shown in FIG. 28, extends in the longitudinal direction of theelongated intermediate top portion 101A of the press formed article 101.As shown in FIG. 29, the heating inductors 111, to which a highfrequency current is applied from the high frequency power supply device125, are disposed at points opposing the two hardening regions 102 ofthe press formed article 101 on a lower face of the cover 122. Theseheating inductors 111 are coupled to each other through the couplingmember 114 which has been explained in FIG. 21, and the respectiveinductive conductors 112 of the heating inductors 111 vertically opposethe hardening regions 102. The heating inductors 111 made of a lowelectrical resistance material such as copper or the like are attachedto the cover 122 with stud bolts 132 piercing retaining bars 131 made ofa nonconductive material such as bakelite or the like and the cover 122made of fire resistive and nonconductive calcium silicate fiber or thelike. Further, insulating members are inserted between the stays 123made of a metallic material such as stainless steel or the like and thestud bolts 132.

The dimension in the direction perpendicular to the longitudinaldirection of the press formed article 101 of the inductive conductors112 shown in FIG. 29 is varied in the longitudinal direction of thepress formed article 101. Therefore, the ratio between the hardeningregions 102 and the non-hardening regions in the direction perpendicularto the longitudinal direction is varied in the longitudinal direction inthe press formed article 101 after hardening.

By adjusting the cover 122 position in the lateral direction in FIG. 29by the operation of the handle 129 shown in FIG. 27, the respectivepositions of the heating inductors 111 are adjusted to the positionsexactly opposing the hardening regions 102. In this position-adjustedstate, the cylinder 130 shown in FIG. 27 is contracted to lower thecover 122, thereby providing the distance of the above-describedpredetermined size between the inductive faces 112A shown in FIG. 29 ofthe inductive conductors 112 and the hardening regions 102. Conversely,the cylinder 130 is expanded to raise the cover 122, thereby releasingthe aforesaid clamping of the clamping device, so that the next pressformed article, in turn, can be set on the supporting face 105A of thesupport 105 by a loading device such as a robot or the like.

It should be noted that although the inductive conductors 112 shown inFIG. 29 are not provided with the insulating coating 17 shown in FIG.23, the inductive conductors 112 in FIG. 29 may also be, of course,provided with the insulating coatings. Further, it is also possible toattach to the inductive faces 112A spacers which securely hold distancesof a predetermined size between the inductive faces 112A of theinductive conductors 112 and the hardening regions 102 when the cover122 is lowered by the contraction of the cylinder 130.

As shown in FIG. 29, the cover 122 has a cross section, in the directionacross the intermediate top portion 101A of the press formed article101, in a cone shape such that the middle portion thereof between thetwo heating inductors 111 is greatly apart upward from the press formedarticle 101. At the middle portion of the lower face of the cover 122, afirst anti-oxidation gas supply pipe 140, which is a firstanti-oxidation gas supply means, is disposed along the longitudinaldirection of the cover 122. The anti-oxidation gas supply pipe 140 isheld by a hold member 141 which is attached with stud bolts 143 to abracket 142 installed between the stays 123 which are provided on theright and left sides in FIG. 29.

The first anti-oxidation gas supply pipe 140 and the hold member 141 areformed of a nonconductive material such as a synthetic resin or thelike, thereby preventing an induction current from being generated inthe anti-oxidation gas supply pipe 140 and the hold member 141 even ifthey extend in a direction parallel to the heating inductors 111.Furthermore, as described above, the anti-oxidation gas supply pipe 140and the hold member 141 are disposed at the middle portion of the cover122 which is greatly apart from the two heating inductors 111.Therefore, even when a high frequency current is applied to theinductive conductors 112 of the heating inductors 111, and the hardeningregions 102 are heated by an induction current generated in thehardening regions 102 of the press formed article 101 due to theapplication of current, the anti-oxidation gas supply pipe 140 and thehold member 141 are prevented from being excessively heated to a fixedtemperature or higher by radiation heat from the inductive conductors112 and the hardening regions 102.

As shown in FIG. 29, there is a distance space S1 between the pressformed article 101 and the cover 122. After the anti-oxidation gas, suchas nitrogen gas or the like, jetting from the first anti-oxidation gassupply pipe 140 is supplied to the distance space S1 to bring thedistance space S1 to a space of the anti-oxidation gas atmosphere,hardening is performed on the hardening regions 102 by application of ahigh frequency current to the inductive conductors 112 of the heatinginductors 111. Further, as is understood from FIG. 28, both end portionsin a longitudinal direction along the intermediate top portion 101A ofthe press formed article 101 of the distance space S1, are open to beopen ends 144. At both end portions in the longitudinal direction of thecover 122 close to the open ends 144, first anti-oxidation gas jet pipes145, which are first anti-oxidation gas jet means, are disposed alongthe cover 122. As shown in FIG. 29, the anti-oxidation gas jetting fromthe anti-oxidation gas jet pipes 145 forms gas curtains at the open ends144, thereby preventing the anti-oxidation gas supplied into thedistance space S1 from flowing out from the open ends 144.

As shown in FIG. 29, the press formed article 101 is set on the support105 with the intermediate top portion 101A upward so that an insidespace S2 is provided inside the intermediate top portion 101A. In thisinside space S2, the cooling pipes 113 are disposed which spray thecooling water to the hardening regions 102. Further, in the inside spaceS2, a second anti-oxidation gas supply pipe 150 is also disposed whichis a second anti-oxidation gas supply means for supplying anti-oxidationgas into the space S2. After the anti-oxidation gas is jetted from thisanti-oxidation gas supply pipe 150 to bring the inside space S2 to ananti-oxidation gas atmosphere, hardening is performed on the hardeningregions 102.

As is understood from FIG. 28, both end portions in a longitudinaldirection along the intermediate top portion 101A of the press formedarticle 101 of the inside space S2, are open to be open ends 151. Atpositions of the support 105 close to the open ends 151, secondanti-oxidation gas jet pipes 152 being second anti-oxidation gas jetmeans are disposed through in the direction across the intermediate topportion 101A of the press formed article 101. As shown in FIG. 29, theseanti-oxidation gas jet pipes 152 are provided with a plurality ofnozzles 152A which are inserted into the supporting face 105A of thesupport 105. The anti-oxidation gas is jetted from the nozzles 152A toform gas curtains at the respective open ends 151, thereby preventingthe anti-oxidation gas supplied into the inside space S2 from flowingout from the open ends 151.

As shown in FIG. 27, the first anti-oxidation gas supply pipe 140, thefirst anti-oxidation gas jet pipes 145, the second anti-oxidation gassupply pipe 150, and the second anti-oxidation gas jet pipes 152 areconnected to an anti-oxidation gas supply path 154 extending from ananti-oxidation gas cylinder 153, and are supplied with theanti-oxidation gas from the anti-oxidation gas cylinder 153respectively.

Further, the cooling pipes 113 are connected to a storage tank 160storing the cooling water therein, through an outward path 161 whichsupplies the cooling water in the storage tank 160 to the cooling pipes113. The cooling water sprayed from the cooling pipes 113 to thehardening regions 102 flows out from the open ends 151 of the insidespace S2 into the aforesaid pan 121 in which the press formed article101 is disposed. The pan 121 is formed with drain holes 121A at thebottom, and the drain holes 121A are connected to the storage tank 160through a homeward path 162.

This forms a circulation path 163 for circulating therein the coolingwater between the storage tank 160 and the pan 121. The pan 121 is amember forming a part of the circulation path 163, so that the coolingwater, which is supplied to the hardening regions 102 of the pressformed article 101, is reused by circulation use.

To an appropriate position of the circulation path 163, morespecifically, to the storage tank 160, a replenishing pipe 164 for thecooling water is connected which replenishes the storage tank 160 withthe cooling water which is evaporated and lost due to spray to thehardening regions 102.

Furthermore, into the storage tank 160, a blow pipe 165 is inserted forblowing the anti-oxidation gas into the cooling water stored in thestorage tank 160. The anti-oxidation gas is blown from the blow pipe 165into the cooling water in the storage tank 160 to remove dissolvedoxygen dissolved in the cooling water. Thus, the blow pipe 165 forms adissolved oxygen removing means 166 for removing the dissolved oxygenfrom the cooling water circulating in the circulation path 163. Sincethe cooling water, which is sprayed from the cooling pipes 113 to thehardening regions 102, has dissolved oxygen removed and since thehardening regions 102 are hardened in the anti-oxidation gas atmospheresformed of the anti-oxidation gas supplied into the distance space S1 andthe inside space S2, hardening can be performed on the press formedarticle 101 while preventing oxidation of the hardening regions 102.

Since the cooling water returning from the pan 121 to the storage tank160 has been raised in temperature due to the spray to the hardeningregions 102, the storage tank 160 is provided with a heat removing means170 for removing heat from the cooling water. The heat removing means170 has a water tank 172 storing therein water circulated to and from acooling tower 171, and a heat exchanger 173 which is installed betweenthe water tank 172 and the storage tank 160. The water cooled in thecooling tower 171 removes heat from the cooling water in the storagetank 160 through the heat exchanger 173.

Note that the cooling tower may be provided along the circulation path163 of the cooling water to remove heat directly from the cooling water.

As shown in FIG. 28, the second anti-oxidation gas supply pipe 150 andthe second anti-oxidation gas jet pipes 152 are connected to a pipe 181linking with the aforesaid anti-oxidation gas supply path 154, throughjoint members 180. The cooling pipes 113 are also connected to a pipe183 linking with the outward path 161 of the aforesaid circulation path163 for the cooling water, through a joint member 182.

This makes it possible to use in common the pipe 181 of theanti-oxidation gas supply path 154 and the pipe 183 of the circulationpath 163 even when the support 105, which is prepared for each of thepress formed articles which is different in shape, length, and so on, isreplaced with another to perform hardening on a press formed articlewhich is different in shape, length, and so on by removing the jointmembers 180 and 182.

The hardening operation on the press formed article 101 by the hardeningapparatus having the above-described configuration is performed asfollows:

First, the loading device such as a robot or the like sets the pressformed article 101 on the supporting face 105A of the support 105, andthe press formed article 101 is clamped on the supporting face 105A withthe clamping device which acts on the fixing members 106. Subsequently,the anti-oxidation gas is supplied from the second anti-oxidation gassupply pipe 150 into the inside space S2, and the gas curtains areformed of the anti-oxidation gas from the second anti-oxidation gas jetpipes 152, at the open ends 151 of the inside space S2. This brings theinside space S2 to the anti-oxidation gas atmosphere. It should be notedthat the supply amount of the anti-oxidation gas from the secondanti-oxidation gas supply pipe 150 to the inside space S2 is set largeat the beginning and then gradually decreased to a fixed amount, therebyexpelling air in the inside space S2 in a short time, resulting inimproved operation efficiency. In addition, the formation of the gascurtains at the open ends 151 prevent the anti-oxidation gas fromflowing out from the inside space S2 to thereby keep the anti-oxidationgas atmosphere in the space S2.

Thereafter, the cover 122 is lowered by the cylinder 130 shown in FIG.27 to be in a state to the press formed article 101 as shown in FIG. 29.Subsequently, the anti-oxidation gas is supplied from the firstanti-oxidation gas supply pipe 140 into the distance space S1, and thegas curtains are formed of the anti-oxidation gas from the firstanti-oxidation gas jet pipes 145, at the open ends 144 of the distancespace S1. This brings the distance space S1 to the anti-oxidation gasatmosphere. Also in this case, the supply amount of the anti-oxidationgas from the first anti-oxidation gas supply pipe 140 to the distancespace S1 is set large at the beginning and then gradually decreased to afixed amount, thereby expelling air in the distance space S1 in a shorttime, resulting in improved operation efficiency. In addition, theformation of the gas curtains at the open ends 144 prevent theanti-oxidation gas from flowing out from the distance space S1 tothereby keep the anti-oxidation gas atmosphere in the space S1.

After the inside space S2 and the distance space S1 which the hardeningregions 102 of the press formed article 101 oppose are brought to theanti-oxidation gas atmospheres as described above, the high frequencypower supply device 125 applies a high frequency current to theinductive conductors 112 of the heating inductors 111. This applicationof current generates an induction current in the hardening regions 102so that the hardening regions 102 are heated, and after the hardeningregions 102 are raised in temperature to a predetermined temperature,the application of current to the inductive conductors 112 is stopped.Then, the cooling water is sprayed from the cooling pipes 113 to thehardening regions 102 which are thus rapidly cooled to thereby undergohardening.

Thereafter, the jet of the anti-oxidation gas from the firstanti-oxidation gas supply pipe 140, the first anti-oxidation gas jetpipes 145, the second anti-oxidation gas supply pipe 150, and the secondanti-oxidation gas jet pipes 152, is stopped, and the spray of thecooling water from the cooling pipes 113 is also stopped.

Then, the cover 122 is raised by the cylinder 130, and the press formedarticle 101 is released from clamping of the clamping device through thefixing members 106 and taken out from the support 105 by the aforesaidloading device.

On the support 105, the next press formed article 101 is set by theloading device, and then hardening on this press formed article 101 isperformed by the same operation as described above, and accordinglyindividual press formed articles 101 are subjected to hardening insequence.

The press formed article 101 taken out from the support 105 by theloading device is sent to a drying step with hot air or the like, tohave the cooling water attached thereto removed. Thereafter, the pressformed article 101 which has been joined by welding to other parts issent to a step for coating that is a subsequent operation after thehardening operation.

Even if the operation step is a step such that the press formed article101 is treated in a predetermined chemical solution before the pressformed article 101 is coated, the operation step can be conducted aspredetermined because the hardening regions 102 have been hardened inthe anti-oxidation gas atmosphere as described above, and the coolingwater sprayed to the hardening regions 102 has the dissolved oxygenremoved, that is, the hardening regions 102 have been hardened with theoxidation thereof prevented.

INDUSTRIAL AVAILABILITY

As described above, a press formed article, and an induction hardeningmethod and an induction hardening apparatus therefor according to thepresent invention are suitable for manufacturing press formed articlessuch as a center pillar and so on for a vehicle which have beensubjected to induction hardening.

1. A press formed article, including an intermediate top portion whichextends in a longitudinal direction and a pair of blade portions whichare both bent from said intermediate top portion and extend in saidlongitudinal direction, with a direction of said bend being a lateraldirection thereof, wherein a hardening region where hardening has beenperformed and a non-hardening region where hardening has not beenperformed are provided longitudinally and laterally within at least saidpair of blade portions and an area ratio between said hardening regionand said non-hardening region in said lateral direction is a ratio forachieving a demanded strength and changes along said longitudinaldirection, wherein said hardening region also exists on both sides ofsaid intermediate top portion in the direction perpendicular to saidlongitudinal direction within said intermediate top portion, anon-hardening region exists between said hardening regions within saidintermediate top portion and said non-hardening region within saidintermediate top portion is formed with a hole.
 2. The press formedarticle according to claim 1, wherein said press formed article is acenter pillar of a vehicle.
 3. The press formed article according toclaim 2, wherein said hardening region is provided at a portion of saidcenter pillar corresponding to a window hole for a window glass in aside door of said vehicle.
 4. The press formed article according toclaim 2, wherein said hardening region is a region which widens towardan end and continuously expands from an upper portion to a lowerportion.
 5. A press formed article, including an intermediate topportion which extends in a longitudinal direction and a pair of bladeportions which are both bent from said intermediate top portion andextend in said longitudinal direction, with a direction of said bendbeing a lateral direction thereof, wherein a hardening region wherehardening has been performed and a non-hardening region where hardeninghas not been performed are provided longitudinally and laterally withinat least said intermediate top portion and an area ratio between saidhardening region and said non-hardening region in the directionperpendicular to said longitudinal direction of said intermediate topportion is a ratio for achieving a demanded strength and changes alongsaid longitudinal direction, wherein said hardening region exists onboth sides in the direction perpendicular to said longitudinal directionwithin said intermediate top portion, said non-hardening region existsbetween said hardening regions within said intermediate top portion andsaid non-hardening region within said intermediate top portion is formedwith a hole.
 6. The press formed article according to claim 5, whereinsaid press formed article is a center pillar of a vehicle.
 7. The pressformed article according to claim 6, wherein said hardening region isprovided at a portion of said center pillar corresponding to a windowhole for a window glass in a side door of said vehicle.
 8. The pressformed article according to claim 6, wherein said hardening regionwidens toward an end and continuously expands from an upper portion to alower portion.
 9. The press formed article according to claim 1, whereina groove is provided in a non-hardening region of the intermediate topportion.
 10. The press formed article according to claim 5, wherein agroove is provided in a non-hardening region of the intermediate topportion.
 11. The press formed article according to claim 1, wherein aconcave groove is provided in the non-hardening region between saidhardening regions.
 12. The press formed article according to claim 5,wherein a concave groove is provided in the non-hardening region betweensaid hardening regions.